This invention relates to the separation of particulate from high temperature, high pressure (HTHP) gas, predominantly in the generation of power for public consumption and in the gasification and combustion of coal. In particular, this invention relates to such separation effected by the formation of a moving granular-bed filter (MGBF) in a filtering vessel having a standleg designed to provide optimum removal of particulate from the gas passed through the filtering vessel. A second stage of filtration, also in granular-bed form, may be provided on the top surface of the MGBF to remove a substantial amount of the particulate which are known to be re-entrained into the flow of clean gas due to the movement of the MGBF.
Typical of the power generation system to which this invention may be adapted are pressurized fluid-bed combustion (PFBC), integrated coal gasification combined cycle (IGCC) and direct coal-fueled turbines (DCFT). However, it is to be understood that this invention may be adapted to purposes other than the generation of power or for use in systems other than PFBC, IGCC or DCFT.
Known moving granular-bed filters are commonly composed of granules as the filtering media. Such known granule systems are packed closely and move at a mass rate of about between 40 times to 100 times the flow of particulate in the gas. In accordance with the teachings of the prior art, the bed media are commonly granules of alumina (Al.sub.2 O.sub.3) or other compounds which are chemically stable at the temperature at which the filtering operation takes place. However, alumina granules and the like are costly and it is necessary to recycle the granules through the bed so as to operate at a reasonable cost. This necessity for recycling of the moving bed media introduces design complexity, demands an unreasonably large plant and militates against sound and reliable operation. In addition, the demand for recycling carries with it the requirement for bed media cleaning, wear of the lift pipe that returns the granules, granule degradation, lift gas recompression, and complexities caused by temperature and pressure drop and pressure balancing.
Typical granular-bed filters are arranged with granule flow downward and gas flow upward. The gas velocity through the unit is limited to levels where the granules will not fluidize because of the upward gas flow. Typical granular bed filters are large in diameter and require complex equipment to distribute granules uniformly to the top surface in order to yield acceptable granule and gas flow through the unit.
Thus, there is a need for an improved filtering system which removes a substantial portion of the particulate from the gas in a reliable and cost effective manner. The present invention provides a system which satisfies that need.